A solid oxide fuel cell (hereinafter referred to as SOFC) is known as a versatile and highly efficient fuel cell. An operating temperature of the SOFC is set to high in order to increase ionic conductivity, so that air discharged from a compressor of a gas turbine can be used as air (oxidant) supplied to a cathode side. Further, a high temperature fuel that cannot be used by the SOFC can be used as a fuel of a combustor of the gas turbine.
Therefore, for example, as described in Japanese Patent Application Publication No. 2009-205930, various combinations of SOFC, a gas turbine, and a steam turbine are proposed as a power generation system that can achieve highly efficient power generation. A combined system described in Japanese Patent Application Publication No. 2009-205930 includes an SOFC, a gas turbine combustor that combusts exhausted fuel gas and exhausted air which are exhausted from the SOFC, and a gas turbine including a compressor that compresses air and supplies the compressed air to the SOFC.